The antitumor activity of some cytokines is well known and described. Some cytokines have already been used therapeutically in humans. For example, cytokines such as IL-2 and IFN-γ have shown positive antitumoral activity in patients with different types of tumors, such as kidney metastatic carcinoma, hairy cell leukemia, Kaposi sarcoma, melanoma, multiple mieloma, and the like. Other cytokines like IFNβ, the Tumor Necrosis Factor (TNF)α, TNFβ, IL-1, 4, 6, 12, 15 and the Colony Stimulating Factors (CFSs) have shown a certain antitumoral activity on some types of tumors.
In general, the therapeutic use of cytokines is strongly limited by their systemic toxicity. TNF, for example, was originally discovered for its capacity for inducing the hemorrhagic necrosis of some tumors, and for its in vitro cytotoxic effect on different tumoral lines, but is subsequently proved to have strong pro-inflammatory activity, which can, in case of overproduction conditions, dangerously affect the human body.
As the systemic toxicity is a fundamental problem with the use of pharmacologically active amounts of cytokines in humans, novel derivatives and therapeutic strategies are now under evaluation, aimed at reducing the toxic effects of this class of biological effectors while keeping their therapeutic efficacy.
Some novel approaches are directed to:    a) the development of fusion proteins which can deliver TNF into the tumor and increase the local concentration. For example, the fusion proteins consisting of TNF and tumor specific-antibodies have been produced;    b) the development of TNF mutants which maintain the antitumoral activity and have a reduced systemic toxicity. Accordingly, mutants capable of selectively recognizing only one receptor have already been prepared;    c) the use of anti-TNF antibodies able to reduce some toxic effects of TNF without compromising its antitumoral activity. Such antibodies have already been described in literature;    d) the use of TNF derivatives with a higher half-life (for example TNF conjugated with polyethylene glycol).
The preparation of TNF derivatives capable of selectively targeting the tumoral sites has recently been reported. For example, a fusion protein has been described, obtained by fusing the gene of the heavy chain of an anti-transferrin receptor mAb and the TNF gene, or a fusion protein of TNF with the “hinge” region of a monoclonal antibody against the tumor-associated TAG72 antigen, or a Fv-TNF fusion protein.
EP 251 494 discloses a system for administering a diagnostic or therapeutic agent, which comprises: an antibody conjugated with avidin or streptavidin, an agent capable of complexing the conjugated antibody and a compound consisting of the diagnostic or therapeutic agent conjugated with biotin, which are administered sequentially and adequately delayed, so as to allow the localization of the therapeutic or diagnostic agent through the biotin-streptavidin interaction on the target cell recognized by the antibody. The described therapeutic or diagnostic agents comprise metal chelates, in particular chelates of radionuclides and low molecular weight antitumoral agents such as cis-platinum, doxorubicin, etc.
EP 496 074 discloses a method which provides the sequential administration of a biotinylated antibody, avidin or streptavidin and a biotinylated diagnostic or therapeutic agent. Although cytotoxic agents like ricin are generically mentioned, the application relative to radiolabelled compounds is mostly disclosed.
WO 95/15979 discloses a method for localizing highly toxic agents on cellular targets, based on the administration of a first conjugate comprising the specific target molecule conjugated with a ligand or an anti-ligand followed by the administration of a second conjugate consisting of the toxic agent bound to an anti-ligand or to the ligand.
WO 99/13329 discloses a method for targeting a molecule to tumoral angiogenic vessels, based on the conjugation of said molecule with ligands of NGR receptors. A number of molecules have been suggested as possible candidates, but doxorubicin only is specifically described. No use of ligands of NGR receptors as cytokines vehicles to induce immuno responses is disclosed.
In WO01/61017 the current inventor describes how surprisingly he has found that the therapeutic index of certain cytokines can be remarkably improved and their immunotherapeutic properties can be enhanced by coupling with a ligand of the aminopeptidase-N receptor (CD13). CD13 is a transmembrane glycoprotein of 150 kDa which is highly conserved in various species. It is expressed on normal cells as well as in myeloid tumor lines, in the angiogenic endothelium and in some epithelia. The CD13 receptor is usually identified as the “NGR” receptor, in that its peptide ligands share the amino acid “NGR” motif.
However, there remains a need for further and improved pharmaceutical compositions and methods for the treatment and diagnosis of cancer.